[Prev][Next][Index][Thread]
wire length, clarification

To: mail11:;atcimcad.enet.decdotcom (atteslatech)

Subject: wire length, clarification

From: I am the NRA <piersonatcimcad.enet.decdotcom>

Date: Mon, 28 Nov 94 21:22:06 EST

>Received: from inetgw1.pa.decdotcom by csndotorg with SMTP id AA20414 (5.65c/IDA1.4.4 for <teslaatgrendel.objincdotcom>); Mon, 28 Nov 1994 19:22:13 0700

Cc: piersonatcimcad.enet.decdotcom
>> Given a bunch of 22 ga. magnet wire and a 4" thin wall PVC pipe for
>> a form, design a coil that works well. I plan on figuring out
>> if the wire diameter will allow between 400 and 1000 turns and
>> produce a coil with a height to width ratio of about 4:1.
>> Then, calculate this length, and figure out the 1/4 wave frequency
>> based on this length.
> How? Its NOT the same as the length of the wire. The wire length will
> turn out to be _roughly_ twice the 1/4 wave, for most coils. That is,
> 100 meters of wire will resonate at 50 meters. ROUGHLY. Ther is cut
> and try here.
On rereading, i find myself unclear in the above. Any frequency has an
associated wave length. Roughly, a single isolated conductor
(1/4 wave over gorund, in radio talk...) will resonate at the point
where it is 1/4 wave long. That is: a one meter wire will be resonant
at 4 meters. (call it 70 MHz, roughly...). But. Take that same wire
and wind it onto a single layer coil. It Now "looks" "longer". It will
now resonate at (roughly) 2 meters (call it 144 MHz...8)>>). The exact
frequency will depend on the length to width ratio, turn spacing, etc.
For tall skinny coils, it tends to 21. For shorter fatter coils it
tends back towards to 11 but does not get there. The math is not
exact.
(The 1/4 wave wire will ALSO resonate at 144, in a different mode,
and 288, and......)
regards
dwp